1. Field of the Invention
The present invention relates generally to emissions control systems for internal combustion engines, and more specifically to an exhaust conditioning system for diesel engines. The present system provides for the reduction of oxides of nitrogen, carbon monoxide, and unburned hydrocarbons, as well as the reduction of carbon particulates in the diesel exhaust, using one or more combination catalytic converters and particulate filters. A shroud surrounds the catalytic converter-filter and other components, to insulate the system and reduce external temperatures.
2. Description of the Related Art
Exhaust emissions from internal combustion engines are recognized to be a very serious environmental hazard, and accordingly, numerous ever more stringent laws and regulations require ever cleaner and purer exhaust emissions from such engines. Regulations directed to the diesel or compression ignition engine have generally not been quite so strict as those directed to spark ignition engines, due to the smaller number of diesel engines in operation and also due to the difficulty in reducing or eliminating the carbon particulates normally emitted by such engines.
Nevertheless, the reduction of exhaust emission products from diesel engines is important, particularly for such engines which are used in confined areas, such as generators in enclosed areas, diesel powered machinery used in the underground mining industry, etc. Obviously, it is critical that exhaust emissions be minimized to the greatest degree possible, particularly in the underground mining environment, where breathable air is absolutely critical and toxic gases such as carbon monoxide cannot be tolerated to any degree whatsoever.
Due to these factors, and the difficulty in reducing exhaust emissions from diesel engines to the required degree, many, if not most, jurisdictions either prohibit or greatly restrict the use of diesel powered machinery in underground mining operations. Those that permit such diesel machinery to be used in underground mining, require extremely strict emissions control for such engines. The Pennsylvania Article II-A Diesel Powered Equipment regulations, for example, require that carbon monoxide emissions be reduced to no more than 100 parts per million (ppm), that carbon particulates be reduced by 95% or more from their otherwise unrestricted output, and that exhaust gas temperatures be reduced to no more than 150 degrees Celsius (302 degrees Fahrenheit). These regulations have heretofore generally been considered to be mutually exclusive, as the reduction of emissions by means of a catalytic converter results in considerable heat output from the converter due to the catalytic reaction which serves to clean the emissions. Moreover, the particulate matter is another problem altogether.
Various means have been attempted to resolve this problem, with the solution generally being to cool the reaction in some manner to reduce the temperatures, while trapping the particulates in a separate filter element or the like and cleaning or disposing of the filter periodically. Water has been used as a filtering element, but the resulting sludge creates a maintenance headache and disposal problem, and water per se does little or nothing to reduce other emissions.
Accordingly, a need will be seen for a means of reducing the exhaust emissions of a diesel engine, particularly an engine in an enclosed environment such as an underground mine, and simultaneously reducing the carbon particulate output and temperature of the exhaust. The emissions and particulate reductions are preferably accomplished by means of a single system, rather than requiring separate catalytic converters and filters, although multiple catalytic converter units for treating different types of exhaust pollutants might be used, if so desired. Moreover, the temperature of the converter(s) and filter(s) combination should be maintained at a sufficiently high level so as to operate efficiently, with the system still producing a relatively cool exhaust at or below the above noted Pennsylvania requirements. A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is presented immediately below.
U.S. Pat. No. 3,645,093 issued on Feb. 29, 1972 to William L. Thomas describes an Air Pollution Control System For Internal Combustion Engines, comprising a combustion chamber into which unburned or partially burned hydrocarbons and/or exhaust products are passed. An air pump forces additional oxygen into the chamber for further combustion of the exhaust products, with an ignition source also being provided. A separate coolant pump is used to circulate a liquid coolant around the outside of the combustion chamber shell. No catalytic converter is disclosed by Thomas. The air pump does not provide any cooling for the system, as does the axial fan of the present exhaust system. Rather, the Thomas air pump creates additional heat by providing further oxidation of exhaust output, thus requiring Thomas to provide cooling for the system using some other means, i.e., liquid.
U.S. Pat. No. 3,820,327 issued on Jun. 28, 1974 to Claude Henault describes a Temperature Regulator For A Catalytic Converter, in which air warmed by passing through an engine coolant radiator, or ambient air, is selectively passed through a shroud around a catalytic converter in order to control the temperature of the converter. While some form of temperature regulation of a catalytic converter used in the present invention could be incorporated, the airflow provided by the cooling fan of the present system is not for cooling the converter-filter, but rather for cooling the outside of the converter canister and surrounding shroud in order to reduce the temperature of the shroud to a point no higher than 150 degrees Celsius.
U.S. Pat. No. 3,967,929 issued on Jul. 6, 1976 to Tsuyoshi Tamazawa et al. describes an Exhaust Gas Purifying System incorporating an air pump for delivering additional air into the exhaust manifold for further oxidation of unburned hydrocarbons and the like, but further incorporating a selector valve for routing the air through a catalytic converter downstream from the exhaust manifold. The theory of operation is that the excess air may be routed through the catalytic converter for cooling the converter if it gets too hot. However, the excess air would serve to oxidize unburned hydrocarbons in the converter, thus further increasing the heat output of the converter. The air delivery system of the present invention circulates around the outside of the converter and filter, between the converter canister and surrounding shroud, to cool the exterior of the shroud below a predetermined level.
U.S. Pat. No. 4,264,344 issued on Apr. 28, 1981 to Otto A. Ludecke et al. describes a Diesel Engine Exhaust Particulate Trap comprising two concentric filter elements, unlike the axially disposed elements of the present system. At least the outer element of the Ludecke et al. device is formed of material such as pleated paper, which is totally unsuitable for use with the heat developed by the catalytic converter-filter element of the present invention. The present invention serves to remove carbon particulates by heating the catalytic converter-filter element(s) sufficiently highly by means of its reactions with carbon monoxide and other exhaust pollutants, to break down and oxidize such carbon particles as they pass through the converter-filter.
U.S. Pat. No. 4,744,217 issued on May 17, 1988 to Dieter Goerlich et al. describes a Particle Separator Arrangement In An Exhaust Pipe Of A Diesel Engine. The device includes a particle trap with further means for providing hot gases into the separator to burn out the carbon particles trapped therein, from time to time. The present invention does not include a separate particulate trap, but rather makes use of the combination filter and catalytic converter(s) used in the system to trap such particulates. The converter-filter(s) operate at a sufficiently high temperature to oxidize any unburned carbon particulates entering the converter, and thereby continuously and automatically clean the converter of particulates once the converter warms to normal operating temperature. The fan means used with the present invention does not cool the converter core, but rather directs cooling airflow around the outside of the converter-filter canister and between the canister and shroud to cool the exterior of the device to no more than a predetermined maximum temperature.
U.S. Pat. No. 5,105,619 issued on Apr. 21, 1992 to Minoru Arai describes a Regeneration System For Particulate Trap, wherein the heating means for the trap is an electric resistance heater. The present system utilizes the existing catalytic converter(s) both to trap particulates as well as to oxidize those trapped particulates by means of the heat generated in the catalytic converter(s). Arai does not disclose a catalytic converter, nor any air ducting around the exterior of the trap, as is provided for cooling the exterior housing of the present system.
U.S. Pat. No. 5,243,819 issued on Sep. 14, 1993 to Siegfried Woerner et al. describes an Exhaust Gas Cleaning Device For Diesel Engines, similar to the particulate separators or traps disclosed by Goerlich et al. and Arai and discussed above. Woerner et al. use a supplementary burner to heat the trap, rather than providing a combination catalytic converter-filter and using the heat of the catalytic reaction to burn off the particulates, as is done in the present invention. Moreover, Woerner et al. provide for the routing of the supplemental burner gases around the outside of the trap, in order to heat the relatively cooler outer portions of the trap. The present invention provides insulation around the catalytic converter canister, which serves (1) to maintain the heat of the converter for more efficient reaction, and (2) to reduce the convected heat to below a predetermined maximum level.
U.S. Pat. No. 5,272,874 issued on Dec. 28, 1993 to Norbert Paas describes an Exhaust Treatment System for mine certified diesel engines, for reducing exhaust emissions, particulates, and cooling the exhaust, as required by regulations. However, Paas goes about the solution to the problem in an entirely different manner than that of the present invention, using a considerably more complex apparatus which requires intermittent cleaning and replacement of certain elements. Paas provides a plurality of relatively small catalytic converters at each exhaust manifold tube, which small converters are inefficient and difficult to heat to the desired temperature for optimum operation, particularly in view of the water cooled exhaust manifold tubes immediately upstream of each of the converters. The present invention preferably utilizes a single combination catalytic converter and filter, or alternatively a series of two or more, rather than a plurality of such converters in parallel, as does Paas. Also, while Paas states that his catalytic converters serve to eliminate some of the particulate matter from the exhaust, he must rely upon a particulate filter downstream of the catalytic converters in order to remove the balance of particulate material, whereas the present system uses the catalytic converters to remove essentially all of the particulate material required to be removed from the exhaust by regulation. No additional filters or other elements are required in the present invention. Paas then circulates the engine exhaust through a heat exchanger in order to cool it sufficiently to pass through a relatively inexpensive disposable filter. However, the carbon buildup within the relatively cool heat exchanger must be handled in some manner. Paas responds to this problem by injecting water into the system from time to time, which flashes to steam to blow the carbon residue from the heat exchanger. While the Paas system does allow a relatively inexpensive, disposable exhaust particulate filter to be used, the apparatus providing for such an inexpensive filter is relatively complex and costly, unlike the present system. Where Paas uses water to cool his exhaust system, the present system is cooled with air, with the cooling medium never entering the exhaust system until the exhaust has been completely processed, at the extreme output end of the system.
U.S. Pat. No. 5,403,557 issued on Apr. 4, 1995 to Harold L. Harris describes an Emission Control Apparatus For Diesel Engine, including a particulate trap and noise reduction device combined in a single unit. The particulate trap is upstream of a separate catalytic converter, to remove substantially all of the particulates from the exhaust gases before they reach the converter, unlike the present invention which utilizes the combination converter and filter to remove particulates in addition to other undesirable exhaust gases. While Harris also provides some sound muffling means with his apparatus, he is silent regarding any means of reducing the exterior temperature of the device. The present system includes external temperature reduction means, comprising a fan for air flow between the insulated catalytic converter canister and a surrounding shroud.
U.S. Pat. No. 5,431,706 issued on Jul. 11, 1995 to Norbert Paas describes a Disposable Particulate Filter generally comprising a pair of concentric, toroidally shaped filter elements. Exhaust passes between the two elements, with filtered exhaust passing either outwardly around the outermost element, or centrally outward from the center of the inner element. Paas notes that experiments wherein the semi-permanent catalytic converter element has been used to trap and oxidize the particulate material from a diesel exhaust have not been successful when such engines are used in light duty cycles (column 1, lines 62-68), but fails to consider insulating the converter to retain heat and to reduce the temperature of the outer shell, as is done in the present invention.
Finally, U.S. Pat. No. 5,488,826 issued on Feb. 6, 1996 to Norbert Paas describes a Heat Isolated Catalytic Converter. This patent is a continuation in part of Paas' earlier issued U.S. Pat. No. 5,272,874, and incorporates a similar catalytic converter structure, with separate converters housed in each exhaust manifold tube from each exhaust port of the engine. However, the continuation patent provides for a pair of annular insulation gaps or spaces concentric with each converter, to reduce heat transfer to the exhaust manifold tubes. It would appear that Paas recognized the shortcomings of the catalytic converter structure of his earlier issued '874 patent, with the relatively small converters in direct contact with the liquid cooled exhaust manifold tubes and resulting inability of the converters to attain sufficient temperature for suitable operation and for achieving the stated purpose of oxidizing some of the particulate matter of the diesel exhaust. However, the plural, relatively small converters of the Paas '826 patent are still considerably more difficult to heat to an optimum operating temperature than the present single converter and filter combination, or plural converters and filters in series, of the present invention, and the liquid cooling provided by Paas further lowers the temperature of adjacent structures to a degree considerably less than that desired or permitted by regulation.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.